class_docstr: Class used for managing plot data
    - allows data sharing between multiple graphics items (curve, scatter, graph..)
    - each item may define the columns it needs
    - column groupings ('pos' or x, y, z)
    - efficiently appendable 
    - log, fft transformations
    - color mode conversion (float/byte/qcolor)
    - pen/brush conversion
    - per-field cached masking
      - allows multiple masking fields (different graphics need to mask on different criteria) 
      - removal of nan/inf values
    - option for single value shared by entire column
    - cached downsampling
    - cached min / max / hasnan / isuniform
code: def min(self, field):
      mn = self.minVals.get(field, None)
      if mn is None:
          mn = np.min(self[field])
          self.minVals[field] = mn
      return mn
  
file_path: pyqtgraph/pyqtgraph/PlotData.py
imports: import numpy
label_desc: Use image node_id 7 for calling the PlotData obj's underlying member method code with example usage: obj.min(field) and returns: mn